Method and apparatus for forming ultrahigh tensile steel

ABSTRACT

Disclosed is an apparatus and a method for forming an ultrahigh tensile steel. The method may include: (a) preparing a blank from a steel plate sheet; (b) cold-forming the blank into a shape corresponding to a desired end-product; (c) fixing the cold-formed materials to a plurality of pallets; (d) moving the pallets into a heating chamber, and heating the materials to a set temperature in the heating chamber; (e) moving the pallets into a cooling chamber, and cooling the materials in the cooling chamber; and (f) straightening dimensions of the materials which have been transformed in the heat treatment process and cooling process.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2012-0119948 filed in the Korean IntellectualProperty Office on Oct. 26, 2012, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a method and an apparatus for formingultrahigh tensile steel. More particularly, the present inventionrelates to a method and an apparatus for forming ultrahigh tensile steelin which a material is formed through a cold-forming process, followedby heating and cooling the cold-formed material, thereby manufacturing aultrahigh tensile steel product.

(b) Description of the Related Art

Recently, applications for ultrahigh tensile steel in the vehicleindustry have increased to make the vehicle body more lightweight andimprove vehicle safety. The method for forming ultrahigh strength steelgenerally includes hot stamping, particularly for the formation ofultrahigh strength steel having tensile strength of over 1500 MPa.

In particular, hot stamping is used to manufacture ultrahigh strengthsteel components with boron steel, which has excellent heattreatability. In general, boron steel is heated to a temperature rangeat which a phase change to austenite occurs, and then the austeniteformed by heating the boron steel is cooled and simultaneously formedsuch that it changes to a martensite phase.

The hot stamping process is applied, in particular, to impart strength.For example, to ensure strength of a center pillar, a roof rail, abumper, and an impact beam of a vehicle. By forming these components ofhigh strength materials, reinforcements which are typically added to thecomponents may be removed. As a result, the weight of the vehicle bodycan be decreased.

However, using the hot stamping process, the entire component is formedof the martensite phase and is adapted to have ultrahigh strength. As aresult, it is difficult to perform subsequent forming and contouringsteps and the like on these ultrahigh strength components. For example,it becomes difficult to trim a metallic pattern to form an edge andflange of the components by shearing so as to form a contour. Further,in the hot stamping process, time spent in the hot forming and coolingstages may be increased and, thus, productivity may be deteriorated.Further, mass production and cross production of vehicle body productsmay be difficult, and quality of the vehicle body product may be notensured because a constant temperature of the material is not easilymaintained.

Alternatively, laser trimming without using the metallic pattern can beapplied. However, manufacturing costs and processing time increase as aresult.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

The present invention provides a method and an apparatus for formingultrahigh tensile steel. In particular, the present invention provides amethod and an apparatus that makes it possible to eliminate lasertrimming, enables mass production and cross production of products, andimproves the quality of the products formed.

According to one aspect, the present invention provides a method forforming an ultrahigh tensile steel that includes: (a) preparing a blankcut from a steel plate sheet; (b) cold-forming the blank to a shapecorresponding to a desired end product (“cold-formed material”); (c)fixing the cold-formed shape into a plurality of pallets; (d) disposingthe pallets within a heating chamber, and heating the cold-formedmaterials to a set temperature in the heating chamber (“heatedmaterial”); (e) moving the pallets into a cooling chamber, and coolingthe heated material in the cooling chamber (cooled material); and (f)straightening and adjusting one or more dimensions of the cooledmaterial which have been transformed in the heat treatment process andcooling process.

According to various embodiments, the blank is formed by to drawpressing, primary trimming, restriking, piercing, and secondarytrimming, which are sequentially performed through a plurality of moldsin step (b).

According to various embodiments, the blank is cold-formed to a shapecorresponding to the desired end product by the plurality of molds in atime frame of within about 6 seconds.

According to various embodiments, the cold-formed shape is fixed by aclamping unit disposed at the pallet instep (c).

According to various embodiments, the cold-formed shape is heated untila temperature thereof reaches about 750-1000° C. in the heating chamberat the step (d).

According to various embodiments, the heated materials are cooled undera nitrogen atmosphere in the cooling chamber in step (e).

According to various embodiments, a coolant is injected by a coolantinjecting unit disposed at the pallet, and the heated material is cooledby the coolant in step (e).

According to various embodiments, the cooled material is fixed to thestraightening machine, and torsion straightening and cross-sectionstraightening of the cooled material are performed at the step (f).

According to another aspect, the present invention provides an apparatusfor forming ultrahigh tensile steel comprising: a cold forming unitconfigured for cold-forming a blank cut from a steel plate sheet to ashape corresponding to a desired end product (“cold-formed material”); aplurality of pallets configured for fixing the cold-formed materialformed by the cold forming unit; a heating chamber adapted to heat thecold-formed material fixed to the pallets to a set temperature (“heatedmaterial”); a cooling chamber adapted to cool the heated material heatedin the heating chamber (“cooled material”); and a plurality ofstraightening machines configured for straightening and adjusting one ormore dimensions of the cooled materials after performing heat treatmentin the heating chamber and cooling in the cooling chamber.

According to various embodiments, the cold forming unit includes: afirst mold configured for performing draw pressing of the blank, asecond mold configured for primarily trimming edges of the blank afterthe draw pressing, a third mold configured for performing restriking ofthe blank after the primary trimming, and a fourth mold configured forperforming piercing and secondary trimming of the blank after therestriking.

According to various embodiments, the pallet includes: a supportingframe; a plurality of storage plates mounted at the supporting frame andincluding a plurality of layers, and being configured for supporting thecold-formed material; and clamp rods disposed to move along upward anddownward directions by a plurality of clamping cylinders fixed to thesupporting frame, wherein a plurality of clamp fingers supporting edgesof the cold-formed material may be integrally formed with the clamp rod.

According to various embodiments, the pallet further includes a coolantinjecting unit disposed at the supporting frame, and configured forinjecting a coolant to the cold-formed material so as to cool thecold-formed material.

According to various embodiments, the supporting frame includes aplurality of vertical shafts configured for supporting each edge of thestorage plate, and a plurality of horizontal shafts configured forconnecting the vertical shafts between each other in a horizontaldirection.

According to various embodiments, the coolant injecting unit includes acoolant supply passage formed in the vertical shaft and the horizontalshaft, and configured to provide communication between the verticalshaft and the horizontal shaft, and injection nozzles mounted at thevertical shaft and the horizontal shaft, and being in connection withthe coolant supply passage so as to allow injection of a coolant to thecold-formed material.

According to various embodiments, the straightening machine includes: aframe; a clamping unit mounted at the frame, and configured for clampingthe cold-formed material; a torsion straightening unit rotatably mountedat the frame in a state of gripping one end of the cold-formed material,and configured for performing torsion straightening of the cold-formedmaterial; and a plurality of cross-section straightening units disposedat both sides with reference to the cold-formed material at the frame,and rotatably mounted at the frame in a state of gripping flangeportions formed at both sides of the cold-formed material, andconfigured for straightening a cross-section of flange portions of thecold-formed material.

According to various embodiments, the clamping unit includes at leastone clamping body mounted movably thereon in upward and downwarddirections by a clamping cylinder.

According to various embodiments, the torsion straightening unitincludes a rotating block rotatably mounted at the frame andcorresponding to the one end of the material, and a first gripperconnected to the rotating block, the first gripper being movably mountedto move along upward and downward directions by a first operatingcylinder, and configured for gripping the one end of the cold-formedmaterial.

According to various embodiments, the torsion straightening unitincludes a driving unit configured for rotating the rotating block. Thedriving unit may include a pinion gear coupled with a rotating shaft ofthe rotating block, a pair of rack bars coupled at an upper side and alower side of the pinion gear, and a pair of second operating cylindersin connection with the rack bars.

According to various embodiments, the cross-section straightening unitincludes: a rotating body rotatably mounted at the frame at both sideswith reference to the cold-formed material; a third operating cylinderfixed to the frame, and hingedly coupled with the rotating body; and asecond gripper connected to the rotating body, and configured orgripping the flange portion of the cold-formed material with the secondgripper.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an apparatus for forming ultrahightensile steel according to an exemplary embodiment of the presentinvention.

FIG. 2 is a perspective view of a pallet according to an exemplaryembodiment of the present invention.

FIG. 3 is a perspective view of a straightening machine according to anexemplary embodiment of the present invention.

FIG. 4 is a perspective view of a clamping unit of a straighteningmachine according to an exemplary embodiment of the present invention.

FIG. 5 and FIG. 6 are drawings showing a torsion straightening unitaccording to an exemplary embodiment of the present invention.

FIG. 7 is a perspective view of a cross-section of a straightening unitof a straightening machine according to an exemplary embodiment of thepresent invention.

FIG. 8 is a partial perspective view of the cross-section straighteningunit of FIG. 7.

FIG. 9 is a perspective view showing an operational condition of thecross-section straightening unit.

FIG. 10 is a flowchart of a method for forming ultrahigh tensile steelaccording to an exemplary embodiment of the present invention.

FIG. 11 is a perspective view showing a pallet of an apparatus forforming ultrahigh tensile steel according to another exemplaryembodiment of the present invention.

<Description of Symbols> 1 blank 2 steel plate sheet 3 cold-formedmaterial 10 cold forming unit 11 first mold 12 second mold 13 third mold14 fourth mold 50, 810 pallet 53 supporting frame 61 clamp rod 69 clampfinger 70 heating chamber 80 cooling chamber 200 straightening machine210 clamping unit 310 torsion straightening unit 410 cross-sectionstraightening unit 871 coolant injecting unit

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variouspreferred features illustrative of the basic principles of theinvention. The specific design features of the present invention asdisclosed herein, including, for example, specific dimensions,orientations, locations, and shapes will be determined in part by theparticular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An exemplary embodiment of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings suchthat a person skilled in the art can easily accomplish it.

As those skilled in the art would realize, the described embodiments maybe modified in various different ways, all without departing from thespirit or scope of the present invention.

Components unrelated to the description will be omitted in order toobviously describe the present invention, and like reference numeralswill be used to describe like components throughout the presentspecification.

Further, in the drawings, the sizes and thicknesses of the componentsare exemplarily provided for the convenience of description, the presentinvention is not limited to those shown in the drawings, and thethicknesses are exaggerated to clearly show several parts and regions.

Terms used in the specification, giving the names of the components in‘first’, ‘second’, ‘third’, etc., is for discrimination of them becausethe names are the same and they are not limited to the order.

It is understood that the term “vehicle” or “vehicular” or other similarterm as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g. fuels derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example bothgasoline-powered and electric-powered vehicles.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items.

Unless specifically stated or obvious from context, as used herein, theterm “about” is understood as within a range of normal tolerance in theart, for example within 2 standard deviations of the mean. “About” canbe understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%,0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear fromthe context, all numerical values provided herein are modified by theterm “about”.

FIG. 1 is a schematic diagram of an apparatus for forming ultrahightensile steel according to an exemplary embodiment of the presentinvention.

Referring to FIG. 1, an apparatus 100 for forming ultrahigh tensilesteel according to an exemplary embodiment of the present invention isconfigured for forming steel having an initial tensile strength ofgreater than about 600 MPa to be used in forming vehicle body componentshaving tensile strengths of greater than about 1500 MPa.

For example, as shown and described in the figures, the apparatus 100for forming ultrahigh tensile steel performs cold forming of a blank 1(FIG. 10, S12) which has been cut from boron steel, (FIG. 10, S11) whichhas excellent heat treatment performance. While the exemplary embodimentis described with specific reference to use of boron steel, it isunderstood that other suitable materials used in forming applicablevehicle body components could also be used. The apparatus then performsheat treatment (FIG. 10, S14) and cooling (FIG. 10 m S15) of thecold-formed material 3 (see FIG. 1) so as to manufacture vehicle bodycomponents having tensile strength of over 1500 MPa.

Herein, the vehicle body components may be any components that maysuitably be formed of ultrahigh tensile steel such as, for example, acenter pillar, a roof rail, a bumper, and an impact beam.

The apparatus 100 for forming ultrahigh tensile steel is adapted toeliminate a laser trimming process, decrease production costs, increasemanufacturing speed, enable mass production and cross production of thevehicle body components, and improve quality of vehicle body components.

In the forming process of the present invention, the apparatus 100 isused to form a material into a shape corresponding to a desiredend-product, followed by trimming, piercing, and further suitable stepsthrough cold forming. Further, according to the present invention, thecold-formed material is heated to a high temperature and is thensubsequently quickly cooled thereby improving the strength of thematerial by about two or three times greater than the strength of thematerial prior to heating and cooling. Further, after the heating andcooling processes, the dimensions of the complete product can bestraightened and adjusted as desired.

As shown in FIG. 1, 1, the apparatus 100 for forming ultrahigh tensilesteel includes a cold forming unit 10, pallets 50, a heating chamber 70,a cooling chamber 80, and straightening machines 200.

As shown, the cold forming unit 10 cold-forms the blank 1 cut from asteel plate sheet 2 to a shape corresponding to a desired end-product.

For example, the blank 1 may be cut to have a suitable size from thecoiled steel plate sheet 2 such that press forming is possible. Inaddition, the coiled steel plate sheet 2 may include cold rolled steel,hot rolled steel, sheradizing cold rolled steel, Al—Si boron alloycoating steel, and so on.

The cold forming unit 10 sequentially performs draw pressing, primarytrimming, restriking, piercing, and secondary trimming of the blank 1.Therefore, the blank 1 is cold-formed to a shape corresponding to thedesired end-product in a short period of time, preferably within about 6seconds.

In particular, the sequential forming processes are performed en blocsuch that the fast manufacturing speed of the cold forming unit 10 issatisfied. In particular the cold forming unit 10 includes a pluralityof molds constructed of an upper mold and a lower mold. According to anexemplary embodiment, the plurality of molds include first to fourthmolds 11, 12, 13, and 14.

The first mold 11 is adapted to perform the draw pressing to the blank1, and the second mold 12 is adapted to perform the primary trimming toedges of the blank 1. As such, unnecessary portions besides the shapecorresponding to the desired end-product can be removed after the drawpressing of the blank 1.

The third mold 13 is adapted to perform the restriking to the blank 1after the primary trimming, and the fourth mold 14 is adapted to performthe piercing and the secondary trimming to the blank 1 after therestriking.

The amount of scrap material from the cold forming unit 10 is large and,thus, the scrap trimming is not easily performed if all edges of theblank 1 are trimmed at the second mold 12. Therefore, the primarytrimming and the secondary trimming may be separately performed throughthe second mold 12 and the fourth mold 14 so as to primarily trim a partof the edges and secondarily trim the rest of the edges.

In addition, the restriking of the blank 1 is performed after theprimary trimming by the second mold 12 in order to reduce thespring-back of the blank 1 after the draw pressing by the first mold 11.

The pallet 50 is adapted to fix a plurality of cold-formed materials 3formed with the shape corresponding to the desired end-product in themolds 11, 12, 13, and 14 of the cold forming unit 10 and to deliver thematerials 3 to a next process.

FIG. 2 is a perspective view of a pallet 50 according to an exemplaryembodiment of the present invention.

Referring to FIG. 1 and FIG. 2, the pallet 50 according to an exemplaryembodiment of the present invention is disposed to move in a desireddirection by a caster 52 mounted at an edge portion of a lower surfaceof a base plate 51.

In addition, multiple pallets 50 are preferably provided for massproduction of the cold-formed product. The pallets 50 can be deliveredto a heating chamber 70 and a cooling chamber 80, which will bedescribed in more detail hereinbelow, by a conveyor (not shown) or othersuitable means.

The pallet 50 includes a supporting frame 53, a plurality of storageplates 57, and clamp rods 61 for clamping.

The supporting frame 53 configured to support the storage plates 57,which will be described in more detail hereinbelow.

As shown, the supporting frame 53 is vertically mounted at a base plate51 which is shown as having a quadrilateral shape, and the supportingframe 53 includes a plurality of vertical shafts 54 supporting each edgeportion of the storage plates 57.

The storage plates 57 are also shown as quadrilateral plates configuredfor supporting the cold-formed materials 3. As shown, the supportingframe 53 is mounted at vertical shafts 54 in a plurality of layers alongupward and downward directions.

A supporting member 59 having a block-like shape for supporting thecold-formed material 3 is mounted at an upper surface of the storageplates 57. The supporting member 59 has a shape corresponding to theshape of the cold-formed material 3, and is fixed to the upper surfaceof the storage plate 57 such that the cold-formed material 3 is suitablypositioned thereon.

As shown, clamp rods 61 are further provided extending vertically andconfigured for clamping the cold-formed material 3 that has beenpositioned on the supporting member 59 of the storage plate 57.

In particular, as shown in FIG. 2, a plurality of clamp rods 61 aremounted at both sides of the supporting frame 53, and are verticallydisposed in an arrangement corresponding to the vertical shafts 54. Theclamp rods 61 are disposed to be movable along upward and downwarddirections by a plurality of clamping cylinders 63 fixed to thesupporting frame 53.

As shown in FIG. 2, the clamping cylinders 63 are mounted to fixingblocks 65 fixed to a lower outer surface of the lower storage plate 57,and the clamp rod 61 is vertically movable within an operating rod ofthe clamping cylinder 63.

The clamp rods 61 are mounted to penetrate guide members 67 disposed atouter edges of both sides of the storage plates 57, and the clamp rods61 are adapted to be movable along upward and downward directions withsupport of the guide members 67.

Herein, clamp fingers 69 may further be integrally mounted at the clamprod 61 and configured for supporting edges (flanges) of the cold-formedmaterial 3 positioned on the supporting member 59.

The clamp fingers 69 may be disposed spaced apart from each other by aset distance at the clamp rod 61 along upward and downward directionscorresponding to each storage plate 57, and are fixed to the clamp rod61.

As shown in FIG. 2, the clamp fingers 69 are formed in a shape of an “L”or “F” and are disposed so as to push edges of the cold-formed material3 positioned on the supporting member 59 by force of the clampingcylinder 63 when the clamp rod 61 is moved downwardly by the clampingcylinder 63.

Meanwhile, the heating chamber 70 is adapted to heat the cold-formedmaterials 3 fixed to the pallets 50 to a set temperature.

The heating chamber 70, which may be a furnace or the like, isconfigured to heat a plurality of cold-formed materials 3 fixed to thepallets 50 to a temperature range of from about 750° C. to about 1000°C. within a short period of time, preferably within about 4 to 5minutes. The cold-formed materials 3 are then delivered from heatingchamber 70 to the cooling chamber 80.

The cooling chamber 80 is configured for quickly cooling the pluralityof cold-formed materials 3 previously heated in the heating chamber 70.

In particular, the pallets 50 delivered from the heating chamber 70 areinserted into the cooling chamber 80. The cooling chamber 80 can beconfigured to receive the pallets 50 from the heating chamber 70 andthen deliver the pallets 50 to a next process. According to an exemplaryembodiment, at the cooling chamber 80, nitrogen gas may be injected intoa space in the chamber and the cold-formed materials 3 can be cooledunder a nitrogen atmosphere.

Hereinafter, construction of the straightening machine 200 of theapparatus 100 will be described in detail in connection with anexemplary embodiment.

The straightening machine 200 is configured for straightening(adjusting) dimensions of the materials 3 after performing heattreatment in the heating chamber 70 and cooling in the cooling chamber80.

FIG. 3 is a perspective view of a straightening machine according to anexemplary embodiment of the present invention.

Referring to FIG. 3, the straightening machine 200 includes a frame 110,a clamping unit 210, a torsion straightening unit 310, and across-section straightening unit 410.

The frame 110 is configured for supporting various constituent elementsof the straightening machine 200, and will be described in more detailhereinbelow.

The clamping unit 210 clamps and fixes the cold-formed material 3 loadedon the frame 110.

FIG. 4 is a perspective view of a clamping unit of a straighteningmachine 200 according to an exemplary embodiment of the presentinvention.

Referring to FIG. 3 and FIG. 4, the clamping unit 210 is mounted at theframe 110 so as to be movable along upward and downward directions.

As shown, the clamping unit 210 includes at least one clamping body 213mounted so as to be movable along upward and downward directions by aclamping cylinder 211.

Multiple clamping bodies 213 may be disposed at the frame 110.

The clamping cylinder 211 is fixedly mounted to a supporting plate 217disposed at an upper side of the frame 110 by a plurality of supportingrods 215.

A moving plate 221 is further mounted at an operating rod 219 of theclamping cylinder 211. The moving plate 221 is guided by the supportingrods 215, and is adapted to move along upward and downward directions.

The clamping body 213 is mounted at a lower surface of the moving plate221, and is movable along upward and downward directions by the movingplate 221 so as to fix the cold-formed material 3.

The clamping body 213 is mounted at a connecting member 223 fixed to thelower surface of the moving plate 221. The clamping body 213 has adifferent shape according to each portion of the material 3, and isformed in a shape corresponding to each portion of the material 3.

The torsion straightening unit 310 rotates in a state of gripping oneend of the material 3 so as to perform torsion straightening to thematerial 3.

FIG. 5 and FIG. 6 are drawings showing a torsion straightening unitaccording to an exemplary embodiment of the present invention.

Referring to FIG. 5 and FIG. 6, the torsion straightening unit 310 isrotatably disposed at the frame 110. In addition, the torsionstraightening unit 310 may rotate in right and left directions.

The torsion straightening unit 310 includes a rotating block 311, afirst gripper 331, and a driving unit 351.

The rotating block 311 is rotatably mounted at the frame 110corresponding to the one end of the cold-formed material 3. In addition,the rotating block 311 may rotate in right and left directions. Asshown, the rotating block 311 may be disposed to rotate in right andleft directions by a rotating shaft 313.

The first gripper 331 grips the one end of the cold-formed material 3.In addition, the first gripper 331 is fixedly mounted at the rotatingblock 311 by a mounting bracket 333, and is disposed to move alongupward and downward directions by a first operating cylinder 335.

The first gripper 331 includes a gripping pad 337 configured for pushingand gripping the cold-formed material 3. As shown, and the gripping pad337 is mounted at an operating rod 336 of the first operating cylinder335.

The driving unit 351 is configured for rotating the rotating block 311in right and left directions around the rotating shaft 313.

As shown, the driving unit 351 includes a pinion gear 353 coupled withthe rotating shaft 313 of the rotating block 311, a pair of rack bars355 coupled at an upper side and a lower side of the pinion gear 353,and a pair of second operating cylinders 357 connected with the rackbars 355.

According to the depicted exemplary embodiment, the rack bars 355 changea rectilinear motion of the second operating cylinder 357 to a rotarymotion of the pinion gear 353.

The second operating cylinder 357 is fixedly mounted at the frame 110,and the rack bar 355 is coupled with an operating rod 358 of the secondoperating cylinder 357. Each operating rod 358 of the pair of operatingcylinders 357 are movable in opposite directions from each other.

In particular, each rack bar 355 is movable in an opposite directionfrom the other so as to rotate the pinion gear 353 in both directionsbased on each operating rod 358 of the second operating cylinder 357which move in opposite directions from each other. Thus, the rotatingshaft 313 may be rotated in the reverse (backward) direction, and therotating block 311 may be rotated in right and left directions.

The cross-section straightening unit 410, which is shown in FIG. 3 andin further detail in FIGS. 7 and 8, rotates in a state of grippingflange portions formed at both sides of the cold-formed material 3 so asto straighten the cross-section of the flange portions of thecold-formed material 3.

FIG. 7 is a perspective view of a cross-section straightening unit 410of a straightening machine 200 according to an exemplary embodiment ofthe present invention. Further, FIG. 8 is a partial perspective view ofthe cross-section straightening unit 410.

Referring to FIG. 7 and FIG. 8 together with FIG. 3, the cross-sectionstraightening unit 410 is plurally disposed at both sides with referenceto the cold-formed material 3 at the frame 110, and is rotatably mountedat the frame 110 in a state of gripping the flange portions formed atboth sides of the cold-formed material 3.

As shown in FIGS. 7 and 8, the cross-section straightening unit 410includes a rotating body 411, a third operating cylinder 431, and asecond gripper 451.

In particular, the rotating body 411 is mounted to rotate in upward anddownward directions at the frame 110 at both sides with reference to thematerial cold-formed 3, and is supported by a supporting block 471disposed at the frame 110 so as to rotate in upward and downwarddirections.

According to the depicted exemplary embodiment, the rotating body 411 isguided by a guide hole 473 disposed at both sides of the supportingblock 471 so as to rotate in upward and downward directions. The guidehole 473 is formed according to a pivot trajectory of the rotating body411. As shown in FIG. 8, the guide hole 473 is coupled with a pair ofrollers 415 disposed at both sides the rotating body 411.

The third operating cylinder 431 is fixedly mounted at the frame 110,and is hingedly connected with the rotating body 411 by a hinge pin 433.

The second gripper 451 is adapted to grip edges (flanges) of thecold-formed material 3, and is connected with the rotating body 411.

As shown in FIG. 9, the second gripper 451 performs cross-sectionstraightening of the flange portion of the cold-formed material 3according to the rotating body 411 as it rotates in upward and downwarddirections by operation of the third operating cylinder 431 in a stateof gripping the flange portion of the cold-formed material 3.

Hereinafter, a method for forming ultrahigh tensile steel according toan exemplary embodiment of the present invention using the apparatus 100for forming ultrahigh tensile steel will be described in detailreferring to the above-mentioned drawings and accompanying drawings.

FIG. 10 is a flowchart of a method for forming ultrahigh tensile steelaccording to an exemplary embodiment of the present invention.

Referring to FIG. 1 and FIG. 10, the blank 1 is cut to have a suitablesize from the coiled steel plate sheet 2 at a process S11.

Herein, the steel plate sheet 2 may include cold rolled steel, hotrolled steel, sheradizing cold rolled steel, Al—Si boron alloy coatingsteel, and so on.

In the process S11, the blank 1 is prepared having a predeterminedweight that is higher than a weight of the desired end-product.

If the weight of the blank 1 is lower than the predetermined weight, aholding portion of the press is insufficient, and thus complete formingis not adequately performed. Further, if the weight is higher than thepredetermined weight, then material is wasted and costs increase.

The blank 1 is cold-formed to the shape corresponding to the desiredend-product by the cold forming unit 10 at a process S12.

At the process S12, the blank 1 is preferably formed according to thedraw pressing, the primary trimming, the restriking, the piercing, andthe secondary trimming processes that are sequentially performed throughthe first to fourth molds 11, 12, 13, and 14.

Herein, the first mold 11 performs the draw pressing of the blank 1, thesecond mold 12 performs the primary trimming to edges of the blank 1after the draw pressing, the third mold 13 performs the restriking ofthe blank 1 after the primary trimming, and the fourth mold 14 performsthe piercing and the secondary trimming of the blank 1 after therestriking.

According to the depicted exemplary embodiment, the draw pressing,primary trimming, restriking, piercing, and secondary trimming of theblank 1 are sequentially performed through the first to fourth molds 11,12, 13, and 14 in the cold forming unit 10. Further, the blank 1 iscold-formed to the shape corresponding to the desired end-product withina short time, preferably within about 6 seconds during which thesequential forming processes are performed en bloc.

If the cold forming of the blank 1 formed by the cold forming unit 10 iscompleted, then the cold-formed materials 3 formed to the shapecorresponding to the desired end-product is loaded on the pallets 50,and the cold-formed materials 3 are clamped and fixed at a process S13.

In further detail, the cold-formed materials 3 which are cold-formed atthe cold forming unit 10 may be provided on the supporting member 59 oneach storage plate 57 of the pallets 50 through a robotic or shuttlesystem.

Then, the clamp rods 61 are moved downwardly by operation of theclamping cylinders 63. Thus, the clamp rods 61 are guided by the guidemember 67, and are moved in the lower position.

Therefore, the clamp fingers 69 of the clamp rods 61 are adapted to pushedges (flanges) of the cold-formed material 3 which is provided on thesupporting member 59 disposed on each storage plate 57 by force of theclamping cylinder 63 so as to fix the flanges of the material 3.

The pallets 50 are then moved into the heating chamber 70 with thecold-formed materials 3 fixed to the pallets 50.

In the heating chamber 70, the materials 3 are heated to temperaturerange of from about 750° C. to about 1000° C. for a short period of time(e.g. for about 4 to 5 minutes) at a process S14.

Herein, the temperature range from about 750° C. to about 1000° C. is astabilizing/transition temperature of austenite. In a case in whichsteel heated by the stabilizing/transition temperature of austenite isquickly cooled, a high strength required of the products of theinvention can be ensured. Further, higher temperatures may beundesirable because a coating layer of the cold-formed material 3 may bevaporized if the heating temperature is higher than about 1000° C.

On the other hand, it is difficult if not impossible to gain a uniformand stable austenite structure if the heating temperature is lower thanabout 750° C.

In addition, the heating time of the cold-formed materials 3 is short,preferably about 4 to 5 minutes, to provide a uniform structure byremoving stress of the material 3 and ensuring uniform processingability in a process after heating. According to several experimentalresults, the amount of generated austenite is insufficient in a casethat the heating time is shorter than about 4 minutes. Further,austenite crystal grains undesirably grow in a case that the heatingtime is longer than about 5 minutes. This growth of the austenitecrystal grain results in a deterioration in the strength of the product.

The pallets 50 are then moved into the cooling chamber 80. According topreferred embodiments, a nitrogen atmosphere is formed in the coolingchamber 80, and the cold-formed materials 3 fixed to the pallets 50 arecooled for about 3 seconds by the nitrogen gas at a process S15.

That is, the cold-formed materials 3 that were previously heated to aset temperature are subsequently quickly cooled by the nitrogen gas inthe cooling chamber 80 such that the cold-formed materials 3 aretransformed to a martensite structure. This provides the cold-formedmaterials 3 with sufficient strength and high tension.

If the heat treatment process and the cooling process of the materials 3are completed, dimensions of the materials 3 transformed during the heattreatment process and the cooling process are straightened/adjusted asdesired by the straightening machine 200 at a process S16.

According to the method and the apparatus 100 for forming ultrahightensile steel, the laser trimming process may be eliminated so as toreduce production cost.

In addition, productivity may be improved, and mass production and crossproduction of the vehicle body components are possible as the formingprocesses may be automatically performed, and the time of the heattreatment and the cooling are short.

Further, the forming quality of the vehicle body components is improvedas the temperature of the material can be constantly maintained at a settemperature.

FIG. 11 is a perspective view showing a pallet of an apparatus forforming ultrahigh tensile steel according to another exemplaryembodiment of the present invention.

Referring to FIG. 1 and FIG. 11, the apparatus 100 for forming ultrahightensile steel according to this exemplary embodiment of the presentinvention does not cool the cold-formed materials 3 by using nitrogengas in the cooling chamber 80. Rather, in this embodiment a pallet 810is included for cooling the materials 3 by using a coolant.

As shown in FIG. 11, the pallet 810 includes a supporting frame 811, aplurality of quadrangular storage plates 813, a plurality of clampers851, and a coolant injecting unit 871.

The supporting frame 811 is configured for supporting the storage plates813. In addition, the supporting frame 811 includes a plurality ofvertical shafts 815 configured for supporting each edge of the storageplates 813, and horizontal shafts 817 for connecting the vertical shafts815 with each other in a horizontal direction.

Herein, the vertical shafts 815 support and connect each edge of thequadrangular storage plates 813, and are vertically disposed. Thevertical shafts 815 may be formed in a shape of a pipe of which an upperend thereof is closed and a lower end is opened.

As shown, the horizontal shafts 817 support the vertical shafts 815. Inaddition, the horizontal shafts 817 correspond to each storage plate813, and connect the vertical shafts 815 with each other in width andheight directions.

The horizontal shafts 817 may be formed in a shape of a pipe of whichboth ends thereof are opened. In addition, both ends are respectivelyconnected with each of the vertical shafts 815, and an interior of thehorizontal shaft 817 is in communication with an interior of thevertical shaft 815.

As shown, the storage plates 813 are quadrilateral plates configured forsupporting the cold-formed materials 3, and the supporting frame 811 ismounted at the vertical shafts 815 in a plurality of layers along upwardand downward directions.

Edges of each storage plate 813 are connected with the vertical shafts815. The vertical shafts 815 respectively penetrate edges of eachstorage plate 813, and are connected (such as by welding or the like) atedges of each storage plate 813.

The clampers 851 are configured for clamping and fixing edges (flanges)of the cold-formed materials 3 provided on each storage plate 813.

The clampers 851 are mounted at the storage plates 813 so as tocorrespond to edges of the cold-formed materials 3 provided on thestorage plates 813.

Each clamper 851 can include a locater (not shown) configured forproperly locating edges of the cold-formed material 3, a clamp body 853configured for restricting edges of the cold-formed material 3, and aclamping cylinder 855 hingedly coupled with the locater and the clampbody 853 and configured for rotating the clamp body 853 by areciprocating motion of an operating rod.

The clamper 851 may be in the form of a conventional clamping devicewhich clamps and restricts a component. Therefore, a detaileddescription of the clamper will be omitted.

The coolant injecting unit 871 is configured to inject a coolant to thecold-formed materials 3 which have previously undergone heat treatmentin a state of clamping by the clampers 851 in the heating chamber 70, tothereby quickly cool the cold-formed materials 3.

The coolant injecting unit 871 is disposed at the supporting frame 811of the pallet 810. In addition, the coolant injecting unit 871 includesa coolant supply passage 881 formed in the vertical shafts 815 and thehorizontal shafts 817 of the supporting frame 811. A plurality ofinjection nozzles 883 are further mounted at the vertical shafts 815 andthe horizontal shafts 817.

According to the exemplary embodiment, the vertical shafts 815 and thehorizontal shafts 817 are formed in a shape of a pipe and the coolantsupply passage 881 is an internal space of the vertical shafts 815 andthe horizontal shafts 817.

The coolant supply passages 881 which are formed in the vertical shafts815 and horizontal shafts 817 communicate with each other. Inembodiments in which the vertical shaft 815 is formed in a shape of apipe with a closed upper end and an open lower end, a coolant flows inthe coolant supply passage 881 through the open lower end.

That is, a coolant inflow portion 885 is formed at the lower end of thevertical shaft 815 such that a coolant flows into the coolant supplypassage 881.

Therefore, a coolant having flowed into the coolant supply passage 881through the coolant inflow portion 885 may flow along the coolant supplypassage 881 in the vertical shafts 815 and the horizontal shafts 817.

The injection nozzles 883 are configured for injecting a coolant to thematerial 3 on the storage plate 813, after the coolant has flowed alongthe coolant supply passage 881 in the vertical shafts 815 and thehorizontal shafts 817.

The injection nozzles 883 are mounted spaced apart along lengthdirections of the vertical shafts 815 and the horizontal shafts 817, andare configured to communicate with the coolant supply passage 881 in thevertical shafts 815 and the horizontal shafts 817.

In particular, a coolant flowing in the vertical shafts 815 through thecoolant inflow portions 885 of the vertical shafts 815 flows along thecoolant supply passage 881, and is injected to the cold-formed material3 on the storage plate 813 through the injection nozzles 883.

According to an exemplary embodiment of the present invention, in thestate that the pallets 810 are moved into the cooling chamber 80, acoolant is injected to the cold-formed materials 3 through the coolantinjecting unit 871 of the pallets 810 from the cooling chamber 80 so asto quickly cool the materials 3.

In addition, in this exemplary embodiment, a coolant such as nitrogengas is not used. Rather, a coolant such as cooling water is injectedthrough the coolant injecting unit 871 disposed at the pallets 810 so asto cool the materials 3. Therefore, construction of the entire systemcan be simplified, and an initial investment cost may be saved.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A method for forming an ultrahigh tensile steelcomprising: (a) preparing a blank cut from a steel plate sheet; (b)cold-forming the blank to a shape corresponding to a desiredend-product, to thereby form cold-formed materials; (c) fixing thecold-formed materials to a plurality of pallets; (d) moving the palletsinto a heating chamber, and heating the cold-formed materials to a settemperature in the heating chamber, to thereby form heated materials;(e) moving the pallets into a cooling chamber, and cooling the heatedmaterials in the cooling chamber, to thereby form cooled materials; and(f) straightening dimensions of the cooled materials.
 2. The method ofclaim 1, wherein in (b), the blank is formed by s draw pressing, primarytrimming, restriking, piercing, and secondary trimming sequentiallythrough a plurality of molds.
 3. The method of claim 2, wherein theblank is cold-formed to the shape corresponding to the desiredend-product by the plurality of molds within about 6 seconds.
 4. Themethod of claim 1, wherein in (c), the cold-formed materials are fixedby a clamping unit disposed at the pallet.
 5. The method of claim 1,wherein in (d), the cold-formed materials are heated until a temperaturethereof reaches about 750-1000° C. in the heating chamber.
 6. The methodof claim 1, wherein in (e), the heated materials are cooled under anitrogen atmosphere in the cooling chamber.
 7. The method of claim 1,wherein in (e), a coolant is injected by a coolant injecting unitdisposed at the pallet, and the heated materials are cooled by thecoolant.
 8. The method of claim 1, wherein in (f), the cooled materialsare fixed to the straightening machine, and torsion straightening andcross-section straightening of the material are performed.
 9. Anapparatus for forming ultrahigh tensile steel, comprising: a coldforming unit configured for cold-forming a blank cut from a steel platesheet to a shape corresponding to a desired end-product, to thereby formcold-formed materials; a plurality of pallets configured for fixing thecold-formed materials formed by the cold forming unit; a heating chamberadapted to heat the cold-formed materials fixed to the pallets to a settemperature, to thereby form heated materials; the cooling chamberadapted to cool the heated materials heated in the heating chamber, tothereby form cooled materials; and a plurality of straightening machinesconfigured for straightening one or more dimensions of the cooledmaterials after heating in the heating chamber and cooling in thecooling chamber.
 10. The apparatus of claim 9, wherein the cold formingunit comprises: a first mold configured for performing draw pressing ofthe blank, a second mold configured for primarily trimming edges of theblank after the draw pressing, a third mold configured for performingrestriking of the blank after the primary trimming, and a fourth moldconfigured for performing piercing and secondary trimming of the blankafter the restriking.
 11. The apparatus of claim 9, wherein the palletcomprises: a supporting frame; a plurality of storage plates mounted atthe supporting frame and including a plurality of layers, and beingconfigured for supporting the material; and a plurality of clamp rodsmovably disposed to move along upward and downward directions by aplurality of clamping cylinders fixed to the supporting frame, wherein aplurality of clamp fingers configured for supporting edges of thecold-formed material are integrally formed with the clamp rod.
 12. Theapparatus of claim 11, wherein the pallet further comprises a coolantinjecting unit disposed at the supporting frame, and configured forinjecting a coolant to the cold-formed materials so as to cool thematerials.
 13. The apparatus of claim 12, wherein the supporting framecomprises a plurality of vertical shafts configured for supporting eachedge of the storage plate, and a plurality of horizontal shaftsconnecting the vertical shafts to each other in a horizontal direction.14. The apparatus of claim 13, wherein the coolant injecting unitcomprises: a coolant supply passage formed in the vertical shaft and thehorizontal shaft, and providing communication between the vertical shaftand the horizontal shaft; and injection nozzles mounted at the verticalshaft and the horizontal shaft, and in connection with the coolantsupply passage so as to inject a coolant to the cold-formed material.15. The apparatus of claim 9, wherein the straightening machinecomprises: a frame; a clamping unit mounted at the frame, and configuredfor clamping the material; a torsion straightening unit rotatablymounted at the frame in a state of gripping one end of the cold-formedmaterial, and configured for performing torsion straightening to thecold-formed material; and a plurality of cross-section straighteningunits at opposing sides with reference to the cold-formed material atthe frame, and being rotatably mounted at the frame in a state ofgripping flange portions formed at both sides of the cold-formedmaterial, and configured for straightening a cross-section of flangeportions of the cold-formed material.
 16. The apparatus of claim 15,wherein the clamping unit comprises at least one clamping body movablymounted along upward and downward directions by a clamping cylinder. 17.The apparatus of claim 15, wherein the torsion straightening unitcomprises: a rotating block rotatably mounted at the frame correspondingto the one end of the cold-formed material; and a first gripperconnected with the rotating block and movably mounted along upward anddownward directions by a first operating cylinder, and configured forgripping the one end of the cold-formed material.
 18. The apparatus ofclaim 17, wherein the torsion straightening unit comprises a drivingunit configured for rotating the rotating block, and the driving unitcomprises a pinion gear coupled with a rotating shaft of the rotatingblock, a pair of rack bars coupled at an upper side and a lower side ofthe pinion gear, and a pair of second operating cylinders connected withthe rack bars.
 19. The apparatus of claim 15, wherein the cross-sectionstraightening unit comprises: a rotating body rotatably mounted at theframe at both sides with reference to the cold-formed material; a thirdoperating cylinder fixed to the frame, and hingedly coupled with therotating body; and a second gripper connected with the rotating body,and configured for gripping the flange portion of the cold-formedmaterial.